Multi-frequency vibration analysis of a mobile underwater robotic arm based on fluid–structure interaction

During operation, mobile underwater robotic arms (URAs) are significantly affected by fluid–structure interaction (FSI) induced by the multi-joint coordinated motion, leading to complex multi-frequency vibrations. In this study, FSI simulation is performed to investigate the segmented deployment process of a mobile URA. The mechanisms for the URA multi-frequency vibrations are explored based on a reduced-order model (ROM) that combines wavelet analysis and multi-resolution dynamic mode decomposition, involving frequency-domain analyses of the hydrodynamic forces, structural deformation, and vorticity field distribution. In addition, a tank experiment is conducted to validate the accuracy of the FSI simulation, and the reliability of the ROM is assessed with the relative root mean square error (below 8%). As is revealed, low-frequency vibrations (0.004–1.281 Hz) are mainly induced by the segmented deployment of the URA, mid-frequency vibrations (2.425–2.5 Hz) are primarily caused by the deformation of the downstream components, and high-frequency vibrations (4.848–9.007 Hz) are closely related to the speed of the mobile platform and unsteady vortex shedding. Therefore, the multi-frequency vibrations of the URA can be effectively suppressed by smoothing the joint deployment process, softening downstream stiffness, and optimizing platform speed. This study provides theoretical guidance for the precise control of mobile URAs during operation.